1. Field of the Invention
This invention relates to the control circuitry for an appliance such as a clothes dryer, and is more particularly concerned with the relay circuit interfacing between the output terminals of an integrated circuit control and the power circuit of the machine to selectively provide distinct modes of machine operation.
2. Description of the Prior Art
Conventional appliances generally have several distinct modes of machine operation which are periodically selected and maintained through control apparatus of the machine. U.S. Pat. No. 3,271,877 issued Sept. 13,1966, and assigned to Controls Company of America shows an example of such a control apparatus which consists of control circuitry utilizing a switching configuration in conjunction with a timer.
A dryer control circuit utilizing an integrated circuit is disclosed in U.S. Pat. No. 3,702,030, Ser. No. 129,008, issued Nov. 7, 1972, and assigned to Whirlpool Corporation. This control circuit has no timer but does require interfacing circuitry between the integrated circuit output terminals and the power circuit of the dryer. An example of such interfacing circuitry where three relays are utilized to achieve four distinct modes of dryer operation is shown in U.S. Pat. Application Ser. No. 358,092, filed May 7, 1973, now U.S. Pat. No. 3,802,091 issuued on Apr. 9, 1974, and also assigned to Whirlpool Corporation.
There are a number of advantages associated with the use of an integrated circuit in the control of an appliance such as a dryer. Integrated circuits are small in size, and the integrated circuit control can be located remotely from the control knob or switch on the machine. Also, there is flexibility with regard to the controls themselves since there is no requirement for a timer dial, and controls such as pushbuttons may therefore be used.
All such integrated circuit controls, however, require circuitry to interface between the integrated circuit output terminals and the power circuit of the dryer as seen in the aforementioned U.S. Pat. No. 3,802,091. The main design criteria with regard to such interfacing circuitry is that it be efficient, reliable and durable while, at the same time, being as inexpensive as possible.